In the melee, images shown by Sky Sports suggested that Olsen had clashed with several home fans, with his club saying that the Swedish goalkeeper had taken a “bang on the back of the head”, but was “completely fine”.
Manchester City have confirmed that they will investigate the indicent and “sincerely apologise” to Olsen.
A statement from Manchester City said: “The Club has launched an immediate investigation and once identified, the individual responsible will be issued with an indefinite stadium ban.”
Greater Manchester Police said two men had been arrested and enquiries were ongoing into reports that Olsen was assaulted by a fan.
The clashes follow high-profile recent incidents during pitch invasions at Nottingham Forest and Everton.
A Nottingham Forest fan was jailed for 24 weeks after pleading guilty to assaulting Sheffield United’s Billy Sharp last week, while police and the Football Association (FA) are investigating after video appeared to show Patrick Vieira, the Crystal Palace manager, kicking out at an Everton fan having been accosted by supporters at Goodison Park on Thursday.
The increase in this sort of incident worries Keane, who fears it may not be long for something even more serious occurs.
Describing fans who have assaulted players and managers as “idiots” and “scumbags”, Keane said on Sky: “It’s a disgrace. We’ve seen it a couple of times at Forest and with Patrick Vieira.
“It’s absolutely disgraceful. It really is and I tell you what – a player or a manager is going to be seriously injured.
“If you’re mad enough to come on and punch a player, then you’re mad enough to come on and do something silly like stab a player. Something crazy will happen. People have come back from Covid and forgotten how to behave themselves.”
It was a position echoed by fellow pundit Gary Neville. The former Manchester United full-back worries that fans may be regressing after significant strides were made towards a more inclusive football supporting environment in grounds over the last few decades.
“Why is it happening?” Neville asked. “The last 30 years we’ve brought the fences down in English football and 99 times out of 100, the fans have respected the fact that you don’t run on the pitch because they enjoy the family environment.
“We’ve obviously got far more children coming to the games, far more women coming to the games, and all of a sudden in these last few weeks and months, we’ve got these idiots not just running on the pitch but attacking players. What the hell are you doing?
“Running on the pitch is obviously delirious because City have won the league, so I get that, but attacking opposition players on the pitch – where has this come from? Why is it happening? I’ve got no idea. It’s absolutely ridiculous.”
The FA has confirmed it will investigate the incident.
The national football governing body released a statement saying it was “very concerned about the rise in anti-social behaviour from fans as we reach the end of the season”.
It added: “Clubs play a vital role in addressing this issue and they need to prevent pitch invasions from occurring, as well as taking their own action against those that break the rules and the law.
“The FA will be seeking to do all that it can to work with clubs as well as addressing the issues from a disciplinary perspective.”